The present invention relates generally to a control valve system for air mattress or air cushion support surfaces and more specifically to a control valve system for air mattresses or support surfaces having a plurality of individually controllable chambers, for example, hospital beds.
Other cushion pressure control designs, which use one valve to isolate the cushion from a manifold, with either pressure or vacuum then applied to the manifold, cannot simultaneously increase the inflation of one cushion while exhausting from another. This means that adjusting the cushions in response to patient movement or changes in bed position takes longer, resulting in reduced comfort and possibly a less effective therapy. Also, this type of design cannot be used for the most effective type of patient rotation systems, which increase the pressure in one rotation cushion while simultaneously decreasing the pressure in another.
Other designs may use multiple valves with independent actuators to achieve the desired control conditions. This requires control wiring and space for each actuator. Also this does not insures that only one of the valves per pair is actuated at one time.
Bed cushions are typically inflated to pressures between 1/2 psi and 1 psi. At these low pressures, the size of the flow opening in the valve must be relatively large in order to pass an adequate volume of air to inflate or deflate the cushion in a reasonable amount of time.
Existing valves which have large flow openings either have very large actuators, or are "pilot operated." A pilot operated valve uses a small actuator such as a solenoid to create a condition that causes a larger valve section to open. An example of this would be to use a solenoid to open a tiny valve which allows pressurized air to flow through into a chamber where it actuates a larger valve by pressing against a diaphragm. This type of pilot operated valve generally requires that the minimum air pressure be 3 psi or higher, in order to create enough force to actuate the larger valve. The types of pressurized air sources that are most desirable for hospital bed cushions (high flow low pressure blowers) do not generally create a high enough pressure to actuate a pilot operated valve unless the pilot device is very large.
Existing direct acting valves typically use electrical solenoids to operate a valve with a small opening. Since these valves are typically designed for higher pressures encountered in industrial and commercial applications, the valve openings are small.
The force acting against the operator for a direct acting valve is typically equal to the pressure the valve is sealing against multiplied by the cross sectional sealing area of the valve (F=P.times.A). In an industrial valve, this force might be 100 psi; if a valve had a cross sectional sealing area of 0.20 inches (a practical area for the flows and pressures required by a hospital bed), the force to be overcome by the actuator would be 20 lbs. However, in a hospital bed, the pressure would be on the order of 1 psi, for a total force of only 0.2 lbs.
Because it is impractical to consider using a solenoid developing 20 lbs. of force due to the physical size and high electrical power consumption in high pressure industrial applications, these valves are generally designed with flow openings (valve orifices) having a cross sectional area of on the order of 0.01 square inches. This size opening is too small for the flow rates required at the lower pressures found in a hospital bed system.
Another limitation of prior art valve control structures is the ability to provide proportional flow control.
The valve seat and valve disk can be designed to be either flat, round or with varying amounts of taper. With a flat valve seat, a small amount of movement from the actuator causes a significant increase in flow through the valve. This type of seat and disk design is most useful when it is desirable to inflate a cushion as quickly as possible, or when it is desirable to create a pressure "pulse" with the sudden opening of the valve to high flow conditions.
As the amount of taper is increased on the valve seat and disk, a smaller change in flow is created for a given movement of the actuator. This makes it possible to control the rate of flow through the valve by controlling the positioning of the actuator. This characteristic is particularly useful in "low air loss" cushions, where air is continuously exiting the cushion through a fixed or variable size orifice. A valve with proportioning characteristics can be actuated to where it just provides sufficient air flow to balance against the loss of air from the cushion. As an alternative, the proportioning valve can be used on the discharge side of the cushion to create a variable size orifice to control the rate of discharge from the cushion.
Another use for the proportional flow control characteristics is to control rotation of the patient on the air cushion support surface. Studies have shown that a slow rotation created by simultaneously inflating one cushion while deflating another cushion is preferable to rapid rotation.
When an on/off type of valve is used to inflate or deflate a cushion, the delay time between sensing that the desired pressure has been reached and the time the valve is closed can cause "overshoot" that requires additional correction and adjustment.
A proportional valve can be opened to a full flow position initially to achieve a high rate of flow, then as the desired pressure is approached, the valve can be changed to a partial flow position to reduce or eliminate the overshoot condition as the pressure sensor and bed controls detect the desired pressure being approached.
Proportional opening of valves will result in smoother initial inflation, avoiding pressure peaks or shock waves that may cause patient discomfort. Controlled proportional opening and closing of valves can also reduce the mechanical and air flow noise caused by valves which suddenly open and close.
In controlling the surface pressures of a multiple zone, bed conditions often arise that make it desirable that some cushions receive a higher rate of air flow than others. This may occur because one cushion has a higher volume than others, because the patient weight shifts from one cushion or set of cushions to another, or because of an operating mode change in the bed (for example, by going into a patient rotation mode).
With on/off valves, this can only be achieved by turning the valves on and off at different rates. Such a method of operation can cause uneven inflation, pressure surges, additional noise and longer response times to achieve the desired cushion inflation rates.
In some circumstances, it is desirable to inflate some zones (e.g., side bolsters, head supports, and rotational cushions) to significantly higher pressures than other zones. This is often accomplished by increasing the pressure levels in the pressure supply manifold to serve the requirements of these "hyperinflated zones". With valve's having proportional control characteristics, it is possible to maintain accurate inflation control to the lower pressure zones by reducing the amount these valves open while the pressure manifold is in a hyperinflation state.
In other cases, the air supply may be limited for certain operational modes. For example, it may be desirable to inflate one or more cushion zones very quickly. If a less critical zone requires pressure at the same time, it may "rob" available air from the system, affecting the performance of the bed in meeting the requirements of the zone needing rapid inflation. Using a proportional valve allows the bed control system to restrict the opening of the less critical valves to allocate available air to the more critical locations.
This air apportioning capability can allow the use of small air sources, which require less electrical power, generate less noise and which occupy less space.
In the air cushion environment, an economic and effective actuator has not been found to proportionally position the valve. Solenoid control have been used for the on/off style control valves. Thus, the systems have not taken advantage of the tapered valve body and valve seat.
A control of an air mattress or cushion according to the present invention provides a unique proportional control valve. The system includes a manifold having at least a supply port, one exhaust port and one outlet port connected to a chamber in the manifold. A supply valve and an exhaust valve are on the manifold having coaxial actuating axes and connected to the supply and exhaust ports respectfully. A common actuator is on the manifold between the supply and exhaust valves so as to move the supply and exhaust valves along their actuating axes. The actuator is a linear actuator having first and second ends spaced from adjacent valve stems of the supply and exhaust valves in the neutral position of the actuator. The linear actuator preferably includes an electric motor. The actuator and valve stems are electrically isolated from each other and complete a circuit when engaged. This provides electrical feedback information. The valve bodies are molded from electrically insulated material.
The supply and exhaust valve each include a body having a first outlet connected to a respective port of the manifold, an inlet and a valve seat having an inlet and an outlet side. A valve element on the outlet side of the seat includes a stem extending therefrom through the valve seat to be engaged at its first by the actuator. A spring biases the valve onto the valve seat. The valve seat and the first outlet of the valve have generally an orthogonal axis. The valve body has a second outlet on the outlet side of the valve seat. The outlet port of the manifold is the second outlet of one of the valves. The second outlet of the other valve is plugged. The valve element and the valve seat include tapered portions. The valve element has a first tapered portion that defines a first rate of change of the size of valve opening and lower than the rate of change of a second tapered portion. The valve element includes a shoulder portion extending radially from the tapered portion. The valve seat has a cross-sectional area in the order of 0.10 to 0.40 square inches.
A second end of the actuator extending from the valve element is one of the seats of the spring. The first end of the actuator extends through and is guided by an aperture in the valve body. The second end of the aperture is received in a guide in the housing. The guide also forms a second stop for the spring. The guide on the housing is either in the outlet port or on the plug of the respective valve housing.
The manifold includes a first and a second portion joined together to form the chamber connecting the valve ports. The first portion includes a flange to which the actuator is mounted. The exhaust and supply valves are mounted to the first portion.
To control a plurality of air cushions, the manifold includes a plurality of chambers, each chamber having a supply and exhaust valve mounted to a supply and exhaust port for each of the chambers. The supply valves have a common supply plenum connected in its inlet. The supply valves and the supply plenum are formed as an integral structure. The exhaust valves also include an integral common supply plenum. The supply plenum may include a divider partitioning the plenum into two supply plenums. Electrical controls are mounted on the manifold and are connected to the actuators for each pair of valves. The electrical controls include a plurality of pressure sensors, each connected to a respective chamber. A pressure sensor is also connected to the supply plenum.
A unique pulsating valve is provided and is used in a system with the control valve for an air mattress with a plurality of bladders.
The pulsating valve includes a supply chamber, exhaust chamber and plenum in a housing. A supply valve and exhaust valve in the housing connect the supply and exhaust chambers respectively to the plenum. Supply and exhaust solenoids are connected to and control the supply and exhaust valves. The valves are in and the solenoids are mounted to an interior housing and are covered by an exterior housing. The exterior housing defines the chambers with the interior housing. The housing includes at least one supply port, one exhaust port and an outlet port and may include additionally a supply outlet.
The solenoids include a coil and a core in a casing and the valves are connected to a first end of the core through a first aperture in the casing. The casing includes a second aperture opposed a second end of the core. The core is substantially hollow along its length. A resilient stop is provided between the casing and the second end of the core to act as a shock absorber. A resilient element is placed between the solenoid and interior housing also to provide isolation and vibration absorption,. Vibration dampening mounts connect the housing to a support surface.
A valve assembly for an air mattress having a plurality of bladders includes a supply inlet, a first valve connected to the supply inlet and at least one outlet to be connected to a first bladder for pulsating air signals to the first bladder. A second valve is provided connected to the supply inlet and least one outlet is to be connected to a second bladder for inflating and deflating the second bladder. The first valve has a supply outlet and the second valve is connected to the supply outlet of the first valve. The second valve includes a linear actuator for positioning the valve and the first valve includes a solenoid for operating the valve. The first valve produces pulses in the range of 1-25 Hertz.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.